The present invention relates to a process for forming a silicon oxide film. More specifically, it relates to a process for forming a silicon oxide film which is useful as an electrical insulating film, dielectric film or protective film as used in LSI, thin-film transistor, photoelectric converter, photosensitive body and the like.
Heretofore, a silicon oxide film has been frequently used as an electrical insulating film, dielectric film or protective film in silicon devices including a semiconductor. In general, as processes for forming these silicon oxide films, there have been known dry processes such as one comprising thermal oxidizing silicon in the air, one comprising forming the film by plasma CVD using a silane gas or a disilane gas in an oxidizing gas such as oxygen or nitric oxide, and one comprising forming the film directly from quartz by sputtering; and wet processes such as one comprising coating alkoxysilane such as tetraethoxysilane in a partially hydrolyzed sol state on a substrate and thermally decomposing it.
However, of these processes, the above dry processes to form a silicon oxide film have the following problems; that is, (a) since it is a gas phase reaction, the generation of particles of impurities in a gas phase causes the contamination of an apparatus or the inclusion of foreign matters, thereby causing low production yield, (b) since the material is in gaseous form, it is difficult to form a film having a uniform thickness on a substrate whose surface is not smooth, (c) productivity is low because the formation of the film is slow, (d) complicated and expensive radio-frequency generator and vacuum apparatus are required in the case of plasma CVD, and (e) they cannot be easily applied to a substrate having a large area.
Further, in these dry processes, since gaseous silicon hydride which is highly toxic and highly reactive is used as the material, it not only is difficult to handle but also requires a sealed vacuum apparatus since it is in gaseous form. In general, these apparatus not only are bulky and expensive but also consume a large amount of energy in a vacuum or plasma system, causing an increase in product cost.
Meanwhile, the above wet process system using a sol-gel reaction is a process which comprises heating a partially hydrolyzed alkoxysilane to cause its dehydration-condensation reaction. Thus, since water is produced as the reaction proceeds, a compact silicon oxide film cannot be easily obtained, and cracks are liable to be produced due to the occurrence of theinternal stress of the film. Further, since the sol-gel reaction requires a high temperatures heating, the process cannot be applied to a plastic substrate having low heat resistance.
Further, JP-B 7-297669 discloses that a silicon oxide film is formed from a film formed of an amic acid containing hydrolyzable silicon atoms by irradiation of ultraviolet light in the presence of ozone. In this process, since a silicon compound containing an amic acid having high heat resistance as an organic component is used as the precursor of the silicon oxide film, the film can be made thick. This process, however, has a point to be improved, which is low productivity caused by a large amount of ultraviolet light required to oxidize and decompose the organic component.
It is an object of the present invention to provide a novel process for forming a silicon oxide film.
It is another object of the present invention to provide a process for forming a silicon oxide film that is suitably used particularly for producing a device having a compact silicon oxide film on a substrate having a large area.
It is still another object of the present invention to provide a process for forming a silicon oxide film easily, which comprises forming a film from the precursor of a silicon oxide film and processing the precursor film in the presence of oxygen and/or ozone.
Still other objects and advantages of the present invention will be apparent from the following description.
According to the present invention, the above objects and advantages of the present invention are achieved by a process for forming a silicon oxide film, comprising:
(1) forming a coating film from at least one polysilane compound selected from the group consisting of cyclotrisilane, cyclotetrasilane, cyclopentasilane, silylcyclopentasilane, cyclohexasilane, cycloheptasilane, monomethylcyclotrisilane, monomethylcyclotetrasilane, monomethylcyclopentasilane, monomethylcyclohexasilane, monomethylcycloheptasilane, monomethylcyclooctasilane, dimethylcyclotrisilane, dimethylcyclotetrasilane, dimethylcyclopentasilane, dimethylcyclohexasilane, dimethylcycloheptasilane, dimethylcyclooctasilane, 1,1xe2x80x2-biscyclobutasilane, 1,1xe2x80x2-biscyclopentasilane, 1,1xe2x80x2-bissilylcyclopentasilane. 1,1xe2x80x2-biscyclohexasilane, 1,1xe2x80x2-biscycloheptasilane, 1,1xe2x80x2-cyclobutasilylcyclopcntasilane, 1,1xe2x80x2-cyclobutasilylcyclohexasilane, 1,1xe2x80x2-cyclobutasilylcycloheptasilane, 1,1xe2x80x2-cyclopentasilylcyclohexasilane, 1,1xe2x80x2-cyclopentasilylcycloheptasilane, 1,1xe2x80x2-cyclohexasilylcycloheptasilane, spiro[2.2]pentasilane, spiro[3.3]heptasilane, spiro[4.4]nonasilane, spiro[4.5]decasilane, spiro[4.6]undecasilane, spiro[5.5]undecasilane, spiro[5.6]undecasilane, spiro[6.6]tridecasilane, hexasila[3]prismane, octasila[4]prismane, decasila[5]prismane, dodecasila[6]prismane, tetradecasila[7]prismane, silicon compounds obtained by partially substituting hydrogen atoms of said bicyclosilanes with alkyl groups, silicon compounds obtained by partially substituting hydrogen atoms of said spirosilanes with alkyl groups and silicon compounds obtained by partially substituting hydrogen atoms of said silaprismanes with alkyl groups; and
(2) oxidizing the coating film by at least one oxidant selected from the group consisting of oxygen and ozone to convert it into a silicon oxide film.
FIG. 1 shows the MS spectrum of the cyclopentasilane obtained in Synthesis Example 2.
FIG. 2 shows the MS spectrum of the polysilane obtained in Synthesis Example 3.